Aftershock Upsets Effort to Repair Plant

TOKYO—An aftershock that shook Japan's northeast region temporarily shut down power supply and makeshift cooling systems at the Fukushima Daiichi plant Monday, highlighting the vulnerability of the crippled facility a month after a massive earthquake triggered the nation's worst nuclear-power crisis.

Cooling functions at three of the plant's six reactors were restored 50 minutes after the temblor that rattled Fukushima and surrounding areas. Regulators said the suspension didn't appear to have caused any significant safety issues.

Still, the latest quake served as a reminder of how lingering aftershocks and the risk of tsunami could easily upset the delicate efforts to stabilize the problems at the stricken plant. The 7.1 magnitude quake centered in a Fukushima town, 65 kilometers south of the plant, and came on the heels of another quake Friday that temporarily shut down power at two other nuclear power plants in the region.

A strong aftershock with a preliminary magnitude of 7.1 rattles northeastern Japan and shakes buildings in Tokyo. Video courtesy of Reuters.

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The overheating reactors at Fukushima Daiichi have two layers of backup functions in case of a power cut—diesel-powered generators and emergency fire pumps—so they can continue receiving cooling water. But these functions require workers to turn them on manually. This became a problem Monday as a tsunami warning forced all workers to move to a shelter on the plant grounds.

"These disruptions must be solved rapidly as a prolonged lack of cooling would easily end the respite they have managed to maintain," said Tetsuo Iguchi, a professor of radiation engineering at Nagoya University.

Two more earthquakes shook Japan early Tuesday, but there were no immediate reports of damage or injuries, with the levels of magnitude smaller than recent aftershocks that have struck.

The Japan Meteorological Agency said the first quake hit the Fukushima area at 8:06 a.m. with a magnitude of 4.0. The second quake struck in the ocean east of Tokyo area at 8:08 a.m. with a magnitude of 6.3, shaking the downtown Tokyo area.

Despite the lesson from the earlier quake and tsunami that rendered the plant's backup cooling systems fully dysfunctional, officials acknowledge the temporary cooling functions at the plant aren't prepared for large tsunamis.

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"We have several power-generating trucks on standby. There are also spare pumps for emergency," Hidehiko Nishiyama, a spokesman for the government's Nuclear and Industrial Safety Agency said after Monday's aftershock. "But the plant itself has no special protection against large tsunami right now," he added. "Right now it is impossible to do anything to improve the defense of the structure. "

A spokesman for Tokyo Electric Power Co., the plan't operator, said the company's efforts are focused on containing the accident: "We don't have capacity right now" to make these temporary functions tsunami-proof, he said. To minimize the potential problem from Monday's power cut, Tepco sent some workers back to their posts to oversee the return of cooling as soon as the projected time of the forecasted tsunami past. This happened before the tsunami warning was officially lifted, so the company posted watchmen for waves as well, the spokesman said.

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A police officer in a protective suit observed a moment of silence Monday for those who were killed by the March 11 earthquake and tsunami, as he searched for victims in Minamisoma, Fukushima prefecture, about 18 kilometers from the damaged Fukushima nuclear power plant.
Reuters

With radiation leaks hampering efforts to install permanent cooling machinery at the plant, the operators are relying on unstable temporary functions to prevent further problems. Among them is the injection of small amounts of water to keep the reactors from heating to dangerous temperatures that would cause further melting of fuel cores, or in worst cases, hydrogen explosions.

In particular, Mr. Iguchi said, the No. 1 reactor faces a high risk of a dangerous flare-up with the termination of water supply like the one occurred on Monday. The temperature and pressure levels in the reactor remain particularly high at No. 1, where two-thirds of its fuel core is exposed. "There could easily be more melting of the core," he said.

Tepco has been injecting nitrogen into the No. 1 reactor to prevent a hydrogen explosion but the injection was suspended after Monday's quake, the company said. Power supplies to the plant's three other reactors were unaffected.

Monday's tremor caused some injuries and damage to many homes exactly one month after March 11 quake that decimated the Tohoku region. Officials said 220,000 households lost power Monday. A mudslide in Iwaki in Fukushima prefecture buried three homes with some people inside. Four people were rescued, according to national broadcaster NHK, and authorities were checking to see if others were buried.

Earlier in the day, Tepco president Masataka Shimizu made a trip to Fukushima to apologize to its people, but met a cold shoulder when he requested a meeting with governor Yuhei Sato.

At the Fukushima plant, operators nearly completed the work of emptying storage facilities for low-level radioactive water, clearing space for more contaminated water that needs to be pumped out of the damaged reactors to enable repair work. In all, more than 10,000 tons of mildly tainted water was dumped into the sea from these facilities over the past several days. Separately, Tepco said that unmanned power shovels and trucks began removing the debris covering the plant grounds as a result of earlier hydrogen explosions that damaged reactor buildings. Such debris has been a source of radiation leaks while at the same time slowing repair work by blocking the paths of heavy machinery.

Aftershocks have continued incessantly since the March 11 quake that killed more than 13,000 people. About 13, 700 are still missing. On April 8, a powerful aftershock shut down power supplies at two nuclear power plants operated by Tohoku Electric Co. in Miyagi prefecture, north of Fukushima. Both plants lost cooling functions for their reactors for up to an hour and 20 minutes. Both had been safely shut down after the March 11 quake, and the temporary loss of cooling didn't result in major problems, such as rises in reactor temperatures, regulators said.

Supplies of electricity are currently easily disrupted in the Tohoku region, as many of its thermal and nuclear power plants have been shut down by the March 11 quake, putting significant stress on the power grid.

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